1. Field of the Invention
The present invention relates to a wireless communication device and a wireless communication method.
2. Related Art Statement
There are many methods compliant with different standards for wireless communication device such as mobile phones today. For example, TDMA and CDMA are widely used as methods for mobile (cellular) phones in Japan.
A wireless communication device is typically designed to conform to one standard method. However, a frequency band available to each standard method for mobile phones, for example, is becoming scarce as more and more mobile phones are being used. Accordingly, attempts are made to shift to multiband methods. Also, in order to provide high capability services, a shift to multiband/multimode is being made in which hand-off between different frequency bands and communications using multiple communication systems (for example cdma2000 1x and cdma2000 1xEV-DO systems) are performed.
By way of such a multiband/multimode-capable wireless communication device, there is a mobile phone which uses, for example, TDMA in combination with CDMA and in which a TDMA-based transmitter-receiver unit and a CDMA-based transmitter are coupled to a primary antenna and a CDMA-based receiver is coupled to a secondary antenna (for example, see Japanese Patent Application Laid-Open No. 2004-15162).
Recently, it is envisioned that multiband/multimode-capable mobile phones include SHDR (Simultaneous Hybrid Dual Receiver) functionality in which transmission and reception in a cdma2000 1xEV-DO system are performed using a primary antenna while reception in a cdma2000 1x system is performed using a secondary antenna in order to improve the throughput of communication through the primary antenna.
FIG. 1 is a functional block diagram schematically showing a configuration of major parts of a mobile phone set ( ) including such an SHDR functionality. The mobile phone set (cellular phone set/portable phone set) has a 1x system (line switching system) using cdma2000 1x in the 800 MHz band (hereinafter often simply referred to as the 800 MHz band) and cdma2000 1x in the 2 GHz band (hereinafter often simply referred to as the 2 GHz band) as well as an EVDO system (packet switching system) using 1xEV-DO. The mobile phone set also has the capability of receiving signals of a GPS frequency of 1575.42 MHz (hereinafter sometimes simply referred to as the 1.5 GHz band). The mobile phone set includes a transmitter (Tx) 101 connected to a baseband unit 100 including a modulating circuit and a demodulating circuit, a primary receiver (primary Rx) 102, and a secondary receiver (secondary Rx) 103.
The transmitter 101 and the primary receiver 102 are connected to a primary antenna 105 through a duplexer 104 and they are capable of transmitting and receiving signals in the 800 MHz band and 2 GHz band. The secondary receiver 103 is connected to a secondary antenna 106 and is capable of receiving signals in the 800 MHz band, 2 GHz band, and 1.5 GHz band independently of the primary receiver 102.
The mobile phone set uses a diversity scheme in communication though the EVDO system (hereinafter sometimes simply referred to as EVDO communication) and periodically receives a notification (paging) which notifies the arrival of an incoming signal from a base station in communication using the 1x system (hereinafter sometimes simply referred to as 1x communication), thus monitoring the arrival of a voice telephony call. As such a operation mode, there are provided a hybrid mode and an SHDR mode using the SHDR function.
In the hybrid mode, as shown in (a) of FIG. 2, the primary antenna 105 is periodically switched to 1x communication during EVDO communication to receive a paging. On the other hand, in the hybrid mode, the secondary antenna 106 also can diversity-receive a paging using 1x communication in synchronization with the primary antenna 105. In the SHDR mode, as shown in (b) of FIG. 2, the primary antenna 105 is allowed to continue EVDO communication while the secondary antenna 106 is periodically switched to 1x communication to receive a paging, thereby monitoring the arrival of an incoming voice call.
As shown in (b) of FIG. 2, the throughput of EVDO communication in the SHDR mode can be improved as compared with the hybrid mode because EVDO communication is continued without switching the primary antenna 105 to 1x communication in the SHDR mode.
However, because the secondary antenna 106 receives signals in three bands, namely 800 MHz, 2 GHz, and 1.5 MHz bands, the antenna gains of the secondary antenna 106 in the 800 MHz and 2 GHz bands in general are lower than those of the primary antenna 105 which transmits and receives signals in two bands, 800 MHz and 2 GHz bands. For example, as shown FIG. 3, the antenna gains of the primary antenna 105 in the 800 MHz and 2 GHz bands are −3 dBi and 0 dBi, respectively, whereas the antenna gains of the secondary antenna 106 in the 800 MHz and 2 GHz are −10 dBi and −3 dBi, respectively. Accordingly, the ability of capturing a paging from a base station in the SHDR mode is lower than that in the hybrid mode.
Therefore, as shown in FIG. 1, conventionally, the actual sensitivity to an incoming signal in 1x communication received at the primary receiver 102 or the secondary receive 103 and input in the baseband unit 100 is compared in a mode selector 108 with upper and lower thresholds of sensitivity to a signal in 1x communication that are stored in a threshold memory 107 beforehand.
The baseband unit 100, the transmitter 101, the primary receiver (primary Rx) 102, and the secondary receiver (secondary Rx) 103 are controlled so that, when the sensitivity to a signal in 1x communication exceeds the upper threshold in the hybrid mode, the hybrid mode switches into the SHDR mode, and when the sensitivity to a signal in 1x communication decreases to become equal to or lower than the lower threshold in the SHDR mode, the SHDR mode switches into the hybrid mode.